1. Department of Radiology and Neurological Surgery, Columbia University, College of Physicians and Surgeons; Neuroendovascular Service, Neurological Institute of New York and New York Presbyterian Hospitals, New York, New York 10032,
2. Doris and Stanley Tananbaum Stroke Center, Columbia University, New York, New York 10032;
3. Department of Radiology and Neurosurgery, University of California at San Francisco, San Francisco, California 94143-0628
4. Department of Neurology, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215;,